1. Field of the Invention
Exemplary embodiments of the present invention relate to an apparatus and method for reducing a radiation power and an electric field generated around a wireless power transfer apparatus using magnetic induction and magnetic resonance.
2. Description of Related Art
Energy is a quantity as the ability to perform work. Energy is a physical term indicating heat, electricity, and power. Various types of energies have been discovered, for example, electric energy, chemical energy, water power energy, and thermal energy. Among the energies, the electric energy can be transferrable through a conductor. It is the most fundamental method of transferring the electric energy.
As another energy transfer method, an electric field has been used for generating electricity. It is a technology of transferring electricity from a 1st coil to a 2nd coil using induced electromotive force generated by a magnetic field and an electric field. Such a technology has been used in a power plant.
Further, a wireless energy transfer method has been introduced. It is a propagation technology transmitting a constant power signal through air. Although such a wireless energy transfer method has been widely used, it is not an effective energy transfer method.
Meanwhile, Massachusetts Institute of Technology (MIT) introduced a new wireless energy transfer technology at 2007. The MIT wireless energy transfer technology uses a magnetic resonance scheme and a magnetic induction scheme.
That is, in the MIT wireless energy transfer technology, power is transferred by inducing magnetic field resonance using two magnetic resonators having the same frequency. Hereinafter, the wireless energy transfer technology introduced by MIT will be described.
FIG. 1 is a diagram illustrating a wireless power transfer apparatus introduced by MIT.
Referring to FIG. 1, a transmission end includes a helical resonance coil 101 and a feeding roof 102 for transmission impendence matching. A receiving end includes elements corresponding to the transmitting end. The receiving end includes a helical resonant coil 103 and a receiving roof 104.
MIT set manufacturing conditions of the helical resonant coil 101 of FIG. 1 as follows.
A diameter (d) of the helical coil 101 is about 60 cm, and the number of turns (n) in the helical coil is 5.25. The height (h) of the helical coil is 20 cm, and a thickness of a line of the helical coil is 6 mm. The feeding roof 102 and the receiving roof 104 are manufactured to have a diameter of 50 cm which is slightly smaller than the helical coils 101 and 103. In this case, a resonant frequency between two helical coils 101 and 103 is about 10.0560.3 MHz.
In the transmission end, the feeding roof 102 and the helical coil 101 are separated from each other at Ks. In the receiving end, the reception coil 103 and the receiving roof 104 are separated at Kd. The receiving roof 104 includes a light bulb in order to confirm that energy is transmitted to air.
However, such as resonance structure generates a radiation power about −11 dBi, and a strong electric field is formed with a magnetic field between two resonant devices. Such a strong electric field is very harmful to human body. Accordingly, it is difficult to commercially use such a technology.